Daylight redirecting window covering

ABSTRACT

An optically transmissive light directing sheeting and daylight control structures employing the same. The light directing sheeting includes a core light redirecting layer employing TIR surfaces embedded into the sheeting and may further include one or more outer layers having light diffusing surface microstructures. The TIR surfaces intercept and reflect a portion of sunlight propagating through the core layer such that the light directing sheeting partially transmits and partially redirects the sunlight towards a plurality of divergent directions, forming relatively high bend angles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/175,952,filed Jun. 7, 2016, which is a continuation of application Ser. No.14/797,102 filed Jul. 11, 2015. This application also claims priorityfrom U.S. provisional application Ser. No. 62/029,374 filed on Jul. 25,2014, incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable

NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION

A portion of the material in this patent document is subject tocopyright protection under the copyright laws of the United States andof other countries. The owner of the copyright rights has no objectionto the facsimile reproduction by anyone of the patent document or thepatent disclosure, as it appears in the United States Patent andTrademark Office publicly available file or records, but otherwisereserves all copyright rights whatsoever. The copyright owner does nothereby waive any of its rights to have this patent document maintainedin secrecy, including without limitation its rights pursuant to 37C.F.R. § 1.14.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to light directing sheeting, films, panelsand light control devices incorporating same. More particularly, thisinvention relates to light directing sheets, panels and films capable ofredirecting off-normal light rays at relatively high bend angles,including bend angles exceeding 90 degrees. This invention furtherrelates to light directing sheet-form materials for the use indaylight-harvesting glazing for enhanced natural illumination ofbuilding interiors or other types of enclosed structures. It alsofurther relates to window coverings, skylights, artificial light controldevices and daylight control devices.

2. Description of Background Art

Various optical films and panels used to redirect light oftenincorporate prismatic surface microstructures such as linear prismarrays and the like. Such prismatic microstructures typically includesurfaces that are not parallel to the prevailing plane of the film orpanel and can thus redirect light by a prescribed angle by means ofrefraction or total internal reflection (TIR).

However, the bend angles that can be achieved using prismaticmicrostructures are limited and typically are below 60 degrees inpractice. Additionally, the exposed micro-prismatic surfaces are proneto soiling and damage. Lamination of such surfaces onto other surfaceswithout impairing the optical performance of the device is problematicdue to the unavoidable air gaps between surface microstructures.Furthermore, micro-prismatic surfaces redirect not only the off-normalrays but also rays that have normal incidence thus impeding the view ofobjects behind such surfaces.

Accordingly, practical light directing sheet materials are needed thatcould be implemented with smooth external surfaces and that can beconfigured to bend light by larger angles. Furthermore, practical lightharvesting and light control devices and systems that employ such lightdirecting sheet materials are also needed. These needs and others aremet within the present invention, which provides an improved sheet-formstructure for redirecting off-normal light rays at high bend angleswithout the need of outer surface texturing and also provides a methodof making the same. The improved sheet-form structure employs internalTIR surfaces to efficiently redirect light and can also be made thin andflexible, finding utility in various light control devices and systems.

BRIEF SUMMARY OF THE INVENTION

The present invention solves a number of light redirecting problemswithin a sheet-form optically transmissive material having a layeredstructure with a soft and elastic polymeric core material sandwichedbetween outer sheets of a rigid plastic or glass material. Apparatusesand methods are described for directing and redistributing light usingsuch sheet-form material. The light redirecting functionality isprovided by an array of thin reflectors embedded into the body of thecore material and configured to reflect at least a portion of lightincident onto the sheet surface from an off-normal direction. In atleast one embodiment, the reflectors comprise deep and narrow channelsformed in a surface of the core material and configured to reflect lightby means of a total internal reflection (TIR). Off-normal light raysintercepted by the reflectors can be redirected at high deflectionangles with respect to the incident direction.

In at least one embodiment, the invention features a light directingsheet having optically transmissive layers including a layer of anelastic material attached a layer of a rigid material and having one ormore arrays of parallel channels formed in its surface and configured toreflect light by means of TIR. In at least one implementation, the lightdirecting sheet includes another layer of a rigid material attached toopposite surface of the elastic layer. In at least one implementation,the layer(s) of a rigid material are permanently bonded or welded to thelayer of an elastic material. In at least one implementation, the lightdirecting sheet features smooth outer surfaces and configured to have atransparent or substantially transparent appearance along at leastnormal viewing angles. In different implementations, the light directingsheet can have various features that alter its optical properties,including but not limited to surface texture, light diffusing features,color tint or filtering features. In different implementations, theelastic material of the light directing sheet can include opticallyclear or translucent plasticized polyvinyl chloride (PVC-P),thermoplastic polyurethane (TPU), various thermoplastic elastomers orsilicones.

According to an aspect of the invention, the TIR channels can bearranges in two parallel arrays crossed at an angle with respect to eachother. In at least one implementation, such channel arrays areperpendicular to each other. In different implementations, the channelarrays are formed in the same layer or in different layers of the sameor different optically transmissive clear materials.

In at least one implementation, the rigid material is selected from thegroup of optically transmissive materials consisting of glass,poly(methyl methacrylate), polycarbonate, polystyrene, rigid polyvinylchloride, polyester, and cyclic olefin copolymer.

In different implementations, the light directing sheet has arectangular shape and each of the plurality of channels is alignedparallel to either a longer or a shorter dimension of the rectangularshape.

According to an aspect of the invention, the TIR channels havesubstantially smooth surfaces characterized by a root mean squaresurface profile roughness parameter of at most about 60 nanometers at asampling length of between 20 and 100 micrometers. According to anotheraspect, a root mean square surface profile roughness parameter of atleast a substantial portion of the surface of each channel is at leastabout 10 nanometers at a sampling length of between 20 and 100micrometers.

In at least one implementation, the thickness of the layer of an elasticmaterial is between 200 micrometers and 2 millimeters.

In at least one implementation, at least one edge of the light directingsheet material is made impermeable to moisture and/or air.

In various implementations, the light directing sheet can be attached tosurfaces of various glazing materials. In one implementation, the lightdirecting sheet is attached to a window of a building façade. In oneimplementation, the light directing sheet is attached to a lighttransmitting surface of a skylight structure. In one implementation, thelight directing sheet is attached to the surface of glazing of agreenhouse structure.

In at least one embodiment, the invention features a method for makingan optically transmissive light directing sheeting. According to oneaspect, the sheeting includes an inner sheet of a soft and flexiblematerial sandwiched between a first and a second outer sheets of rigidmaterial, where the inner sheet including a plurality of narrow channelsconfigured to reflect light by means of a total internal reflection. Inat least implementation, the method includes a step of forming at leastone array of substantially parallel slits in the inner sheet, a step ofstretching the inner sheet in a direction perpendicular to the slits,and a step of bonding a major surface of the inner sheet to a majorsurface of the first outer sheet. In at least implementation, the stepof forming at least one array of substantially parallel slits includes aprocess of slitting the surface of the inner sheet with one or morerazors or rotary blades. In at least implementation, the method furtherincludes a step of bonding an outer surface of the inner sheet to thesecond outer sheet.

In various embodiments the invention also features different devices forredistributing the light beam emitted by various sources.

In at least one embodiment, the invention features a lighting fixtureincluding a light source, a sheet of optically clear plastic materialhaving a plurality of linear reflectors embedded into the material,where each of the linear reflectors has at least one surface configuredto intercept at least a portion of light emanated by the light sourceand reflect such portion of light by means of a total internalreflection.

In at least one embodiment, the invention features a window coveringincluding a multi-layer sheet of an optically transmissive materialhaving a first and a second outer layers of a rigid material and a corelayer of a soft material. The core layer includes a plurality of linearreflectors aligned parallel to a reference line and configured todeflect light propagating through the sheet by means of a total internalreflection.

In at least one embodiment, the invention features a slat of a window ordoor blinds system. Such slat includes a strip of an optically clearplastic material having a plurality of linear reflectors embedded intothe material where each of the linear reflectors has at least onesurface configured to reflect light by means of a total internalreflection. In different implementations, each of the linear reflectorsis aligned either parallel or perpendicular to a longitudinal dimensionof the strip.

In at least one embodiment, the invention features a light redirectingawning including a sheet of an optically clear and flexible materialstretched over a frame and having a plurality of parallel linearreflectors embedded into the flexible material, where each of thereflectors has at least one surface configured to reflect light by meansof a total internal reflection.

In at least one embodiment, the invention features a light redirectingskylight structure including a plurality of optically transmissive vanesincorporated into a planar horizontal array, where each of the vanes ispositioned at an angle with respect to a horizontal plane and comprisesthe light directing sheet material having a plurality of internalreflectors extending perpendicular to a vane surface. In variousimplementations, the optically transmissive vanes are arranged into oneor more asymmetric or symmetric arrays. In at least one implementation,the optically transmissive vanes make an angle of less than 45 degreeswith respect to a horizontal plane. In at least one implementation, theangle is less than 30 degrees.

In at least one embodiment, the invention features a light redirectingskylight insert, including the light directing sheet having a thicknessof less than 1.5 millimeters. In different implementation, the shape isa truncated pyramid, a truncated cone, a combination thereon or a nestedarray of such shapes.

Further embodiments and elements of the invention will be brought out inthe following portions of the specification, wherein the detaileddescription is for the purpose of fully disclosing preferred embodimentsof the invention without placing limitations thereon.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The invention will be more fully understood by reference to thefollowing drawings which are for illustrative purposes only:

FIG. 1 is a schematic cross section view of a layered light directingsheet material, according to at least one embodiment of the presentinvention.

FIG. 2 is a schematic perspective view of a light directing sheet havinga rectangular shape, according to at least one embodiment of the presentinvention.

FIG. 3 is a schematic top view of a light directing sheet, showing aplurality of substantially parallel channels aligned along a commonreference line, according to at least one embodiment of the presentinvention.

FIG. 4 is a schematic view of a strip of a light directing sheetmaterial, showing light directing channels extending parallel to ashorter dimension of the strip, according to at least one embodiment ofthe present invention.

FIG. 5 is a schematic view of a strip of a light directing sheetmaterial, showing light directing channels extending parallel to alonger dimension of the strip, according to at least one embodiment ofthe present invention.

FIG. 6 is a schematic cross section view and raytracing of a lightdirecting sheet material, according to at least one embodiment of thepresent invention.

FIG. 7 is a schematic cross section view and raytracing of a lightdirecting sheet material, showing a textured surface formed in an outerlayer, according to at least one embodiment of the present invention.

FIG. 8 is a schematic view illustrating a method of making a lightdirecting sheet material, showing steps of slitting a sheet of soft andelastic material using a blade or razor, stretching the sheet in adirection perpendicular to the slits, and laminating the processed sheetbetween two outer sheets of a rigid material, according to at least oneembodiment of the present invention.

FIG. 9 is a schematic top view of a light directing sheet, showing twolinear arrays of parallel slits crossed at a right angle with respect toeach other, according to at least one embodiment of the presentinvention.

FIG. 10 is a schematic perspective view of a portion of a multi-layerlight directing sheet material, showing perpendicular arrays of parallelchannels firmed in an inner layer of the material, according to at leastone embodiment of the present invention.

FIG. 11 is a schematic perspective view of a portion of a multi-layerlight directing sheet material, showing perpendicular arrays of parallelchannels firmed in different inner layers of the material, according toat least one embodiment of the present invention.

FIG. 12 is a schematic perspective view of sheet of a light directingmaterial having a transparent appearance, according to at least oneembodiment of the present invention.

FIG. 13 is a schematic perspective view of a window pane having a lightdirecting sheet attached to its surface, according to at least oneembodiment of the present invention.

FIG. 14 is a schematic perspective view of a window pane and a windowcovering employing a light directing sheet, according to at least oneembodiment of the present invention.

FIG. 15 is a schematic view showing the operation of a window coveringemploying a light directing sheet, according to at least one embodimentof the present invention.

FIG. 16 is a schematic view showing an embodiment of a window coveringincluding a light redirecting area and an opaque area, according to atleast one embodiment of the present invention.

FIG. 17 is a schematic view showing an embodiment of a window coveringincluding a flexible sheet of a light redirecting materials and a pairof material-holding bars, according to at least one embodiment of thepresent invention.

FIG. 18 is a schematic perspective view of a light-redirecting awning,showing a light directing sheet stretched over a frame of the awning,according to at least one embodiment of the present invention.

FIG. 19 is a schematic perspective view explaining the operation of alight-redirecting awning, according to at least one embodiment of thepresent invention.

FIG. 20 is a schematic view and raytracing diagram showing a lightdirecting sheet disposed at a light output opening of a skylight,according to at least one embodiment of the present invention.

FIG. 21 is a schematic view and raytracing diagram showing a lightdirecting sheet attached to a light emitting opening of a tubularskylight, according to at least one embodiment of the present invention.

FIG. 22 is a schematic view and raytracing diagram showing a prismaticskylight having a light directing sheet attached to its slopedlight-harvesting surface, according to at least one embodiment of thepresent invention.

FIG. 23 is a schematic view and raytracing diagram showing a greenhousehaving a light directing sheet attached to a roof surface, according toat least one embodiment of the present invention.

FIG. 24 is a schematic view and raytracing diagram showing a greenhousein an alternative configuration and orientation, according to at leastone embodiment of the present invention.

FIG. 25 is a schematic perspective view and raytracing of a lightingdiffuser lens employing a light directing sheet and having a rectangularcross section, according to at least one embodiment of the presentinvention.

FIG. 26 is a schematic perspective view and raytracing of a lightingdiffuser lens employing a light directing sheet and having a truncatedpyramid shape, according to at least one embodiment of the presentinvention.

FIG. 27 is a schematic perspective view and raytracing of a lightingdiffuser lens employing a light directing sheet and having a cylindricalshape, according to at least one embodiment of the present invention.

FIG. 28 is a schematic perspective view and raytracing of a lightingdiffuser lens employing a light directing sheet and having a truncatedconical shape, according to at least one embodiment of the presentinvention.

FIG. 29 is a schematic cross section view and raytracing of a downlightmodule configured for direct/indirect lighting, according to at leastone embodiment of the present invention.

FIG. 30 is a schematic perspective view of a slat or blade of windowblinds, showing a plurality of channels configured for redirecting lightby a total internal reflection, according to at least one embodiment ofthe present invention.

FIG. 31 is a schematic perspective view of vertical window blinds,showing a plurality of light deflecting slats, according to at least oneembodiment of the present invention.

FIG. 32 is a schematic fragmentary perspective view of horizontal windowblinds employing light directing sheeting, showing a plurality ofadjustable light deflecting slats, according to at least one embodimentof the present invention.

FIG. 33 is a schematic fragmentary cross section view of horizontalwindow blinds employing light directing sheeting, showing a plurality ofadjustable light deflecting slats in a fully open position, according toat least one embodiment of the present invention.

FIG. 34 is a schematic fragmentary cross section view of horizontalwindow blinds employing light directing sheeting, showing a plurality ofadjustable light deflecting slats in a fully closed position, accordingto at least one embodiment of the present invention.

FIG. 35 is a schematic fragmentary cross section view of horizontalwindow blinds employing light directing sheeting, showing a lightredirecting sheet positioned at an angle with respect to a horizontalplane, according to at least one embodiment of the present invention.

FIG. 36 is a schematic cross section view and raytracing of a skylightdome portion, showing a light redirecting sheet positioned at an anglewith respect to a horizontal plane, according to at least one embodimentof the present invention.

FIG. 37 is a schematic cross section view and raytracing of a skylightdome portion, showing a plurality of light redirecting slats or louvers,according to at least one embodiment of the present invention.

FIG. 38 is a schematic cross section view and raytracing of a skylightdome portion, showing a plurality of light redirecting slats or louversarranged in two symmetrically disposed arrays, according to at least oneembodiment of the present invention.

FIG. 39 is a schematic perspective view and raytracing of a lightredirecting skylight insert shaped in the form of a truncated pyramid,according to at least one embodiment of the present invention.

FIG. 40 is a schematic perspective view and raytracing of a lightredirecting skylight insert having a truncated conical shape, accordingto at least one embodiment of the present invention.

FIG. 41 is a schematic perspective view and raytracing of an array ofnested light redirecting structures each having a truncated pyramidalshape, according to at least one embodiment of the present invention.

FIG. 42 is a schematic perspective view and raytracing of an array ofnested light redirecting structures each having a truncated conicalshape, according to at least one embodiment of the present invention.

FIG. 43 is a schematic top view of a light redirecting sheet having astraight edge and a curved edge, according to at least one embodiment ofthe present invention.

FIG. 44 is a schematic perspective view and raytracing of lightredirecting structures for use in a skylight, showing a curvedthree-dimensional shape for each of the structure, according to at leastone embodiment of the present invention.

FIG. 45 is a schematic perspective view and raytracing of lightredirecting structures for use in a skylight, showing an alternativecurved three-dimensional shape for each of the structure, according toat least one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring more specifically to the drawings, for illustrative purposesthe present invention is embodied in the apparatus and method generallyshown in the preceding figures. It will be appreciated that theapparatus and method may vary as to configuration and as to details ofthe parts without departing from the basic concepts as disclosed herein.Furthermore, elements represented in one embodiment as taught herein areapplicable without limitation to other embodiments taught herein, and incombination with those embodiments and what is known in the art.

The present invention particularly seeks to provide a sheet-form lightcontrol material capable of angularly selective redirection ofoff-normal rays and to further provide illumination components employingsuch material. The material can be configured to transmit a portion ofthe incident light and redirect transmits a portion of the incidentlight with the proportions between the transmitted and redirected lightdepending on the angle of incidence and controlled by the materialstructure. The material can also be configured to deflect light atvariable bend angles depending on the angle of incidence andparticularly provide higher bend angles for relatively high angles ofincidence.

The following embodiments of the present invention are generallydirected to a sheet-form optical article or system which may beconfigurable for light redirecting operation in response to lightincident onto such optical article or system from directions other thannormal and may be further configurable for a generally unimpeded passageof light incident from a normal direction.

FIG. 1 illustrates a first embodiment of a light directing sheeting ofthe invention. In this embodiment, a light directing sheet 2 has amulti-layer structure and is formed by a first outer sheet 40, a secondouter sheet 60, and an intermediate third sheet 4 sandwiched betweensheets 40 and 60. The inner sheet 4 is defined by a first major surface10 and an opposing second major surface 12. The first outer sheet 40 isdefined by a major surface 42 facing away from sheet 4 and an opposingmajor surface 44 facing sheet 4. The second outer sheet 60 is defined bya major surface 62 facing sheet 4 and an opposing major surface 64facing away from sheet 4. Accordingly, major surfaces 42 and 64 of therespective sheets 40 and 60 define opposing outer boundaries of lightdirecting sheet 2.

Sheets 4, 40, and 60 should be made from optically transmissivematerials. Such materials should preferably be optically clear or atleast translucent with relatively high light transmissivity so thatsheet 2 can effectively transmit at least a substantial portion of lightthat enters onto either one of the outer surfaces 42 and 64.

The outer sheets 40 and 60 are made from rigid materials. Preferredmaterials for layers 40 and 60 include but are not limited to glass,poly(methyl methacrylate) (PMMA, acrylic), polycarbonate, polystyrene,rigid polyvinyl chloride, polyester, and cyclic olefin copolymer.

Sheet 4 is made from a relatively soft, flexible and highly elasticmaterial. Such material can be exemplifies by plasticized polyvinylchloride (also frequently referred to as PVC-P, plasticized PVC,flexible PVC or simply vinyl), thermoplastic polyurethane (TPU), andsilicone rubber. More broadly, suitable materials for layer 4 mayinclude various Thermoplastic Elastomers (TPEs) that can be repeatedlystretched to a considerable relative elongation with an ability toreturn to their approximate original length when stress is released. Thematerial selected for layer 4 should preferably be optically clear butmay also have some tint or haze that do not substantially impair itslight transmissive properties.

The thickness of sheet 4 may be selected from a range of thicknessesthat is typical to films or thin sheets of plastic materials. Accordingto a preferred embodiment, the thickness of sheet 4 is between 200micrometers and 2 millimeters.

Sheets 40 and 60 may be bonded to the respective surfaces of sheet 4using optically transmissive adhesives. For example, referring to FIG.1, sheet 40 may be bonded to surface 10 of sheet 4 with an opticallyclear adhesive layer 20 and sheet 60 may be bonded to the opposingsurface 12 of sheet 4 with an optically clear adhesive layer 30.

The major surfaces of sheet 4 may have a smooth finish and may also becalendered for high gloss and optical transmissivity. Alternatively,either one or both major surfaces of sheet 4 may have some roughness topromote adhesion. However, such roughness should normally be kept to aminimum in order to maintain high overall transmissivity of sheet 2. Theouter surfaces 42 and 64 may also be made smooth with a gloss finish orcan be provides with a functional or decorative texture.

The rigidity of the outer sheets 40 and 60 should be sufficient toprovide at least some minimum flexural rigidity and dimensionalstability to sheet 2. Other structural functions of sheets 40 and 60 mayinclude but are not limited to maintaining a planar or other pre-definedthree-dimensional shape of sheet 2 as well as preventing wrinkling,elongation or excessive flexing of the panel which may otherwise resultfrom employing soft and flexible materials, such as for example, TPU orplasticized PVC, for the inner sheet 4. It will be appreciated that thelayered sandwich structure of sheet 2 may result in such panel having aconsiderably greater flexural rigidity compared to the individual sheets40 and 60 and may even exceed the combined flexural rigidity of suchsheets when used individually. In most applications, the flexuralstiffness of common rigid plastic materials such as polycarbonate, rigidPVC, polyester or acrylic of comparable thickness should be deemedsufficient for finished sheet 2.

Since the thickness of a rigid sheet significantly impacts its flexuralrigidity, the thickness of sheets 40 and 60 should be appropriatelyselected based on the desired application and the overall dimensionalparameters of panel 4. In one embodiment, at least one of sheets 40 and60 may have the thickness of at least one fifth of the thickness ofsheet 4. For example, when the thickness of layer 4 is around 1millimeter, the thickness of layer 40 may be 200 micrometers or greater.However, it should be understood that various applications may requiresuch minimum thickness of sheet 40 and/or 60 to be different, e.g., 0.5mm, 1 mm, 1.5 mm, 2 mm, etc.

In some cases, flexing of panel 4 may need to be even further minimizedor almost eliminated. For example, when sheet 40 is made from glass,even limited bending may result in breakage of the sheet. In anotherexample, sheet 2 may be required to maintain strictly planar shape evenat some loads. In such cases, the thickness of sheet 40 can be made 3-4millimeters or more. Substantially greater thicknesses (e.g., 6 mm ormore) may be needed when sheet 2 form a panel that is several metersacross.

Referring yet further to FIG. 1, sheet 4 includes a plurality ofsubstantially parallel, narrow channels 6 extending into the material ofthe sheet perpendicularly to surface 10 (and thus perpendicularly to theprevailing plane of sheet 2). Each channel 6 has parallel ornear-parallel opposing walls 7 and 8 spaced apart by a relatively smalldistance.

The distance between walls 7 and 8 should be substantially less than thedepth of the channel. According to an embodiment of the presentinvention, the depth of each channel 6 may be at least approximately tentimes the average width of the channel. By way of example and notlimitation, the average width of each channel 6 may be approximately 20micrometers or less and the depth of the channel may be at least 200micrometers. In at least some embodiments, the ratio between the depthand width of channels 6 may be advantageously selected to exceed 15 or20 times. It may be appreciated that, since sheet 4 is sandwichedbetween rigid sheets 40 and 60, channels 6 disposed between surfaces 10and 12 can be protected from the environment and resist soiling andmoisture ingress. Furthermore, the rigid sheets 40 and 60 can ensurethat the opposing walls 7 and 8 of channels 6 do not close upon eachother when sheet 2 is subjected to stresses or deformations during use.

Each of the walls 7 and 8 should have a substantially smooth surfacecapable of reflecting light by means of a total internal reflection in aspecular or near-specular regime while minimizing scattered light. Itshould be understood that the surfaces of walls 7 and 8 do not have tobe absolutely smooth to provide such operation. It can be shown thatwalls 7 and 8 may provide good reflectivity even with somenon-negligible surface roughness as long as such roughness issignificantly less than the wavelength. According to one embodiment, aroot-mean-square (RMS) roughness parameter of the surface of walls 7 and8 may be within the range between 0.01 micrometers (10 nanometers) and0.06 micrometers (60 nanometers), and more preferably between 0.01micrometers (10 nanometers) and 0.03 micrometers (30 nanometers). Thepreferred sampling length for measuring such RMS roughness parametershould be between 20 and 100 micrometers and should not generally exceedthe depth of channels 6.

By way of example, the inner sheet 4 may have a general structure,operation and/or manufacturing method described in U.S. Pat. No.9,007,688 to Vasylyev (issued Apr. 14, 2015), herein incorporated byreference in its entirety. It is noted that, where a definition or useof a term in a reference, which is incorporated by reference herein isinconsistent or contrary to the definition of that term provided herein,the definition of that term provided herein applies and the definitionof that term in the reference does not apply.

Referring to FIG. 2, sheet 2 may have a generally planar appearance anda rectangular shape. One or more edges of sheet 2 may be sealed using anair and/or moisture impermeable encapsulating resin or tape. In oneembodiment, the entire perimeter of sheet 2 may be sealed which couldprevent layers delamination, moisture ingress and/or contamination ofchannels 6 with dirt or dust.

While sheets 4, 40 and 60 are shown having identical dimensions in FIG.2, it should be understood that such sheets may have differentdimensions as well. For instance, according to at least one embodiment,one of the sheets may have greater or smaller width and/or length withrespect to the other two sheets. In a more specific non-limitinginstance, one or both major dimensions of sheets 4 and 40 may be smallerthan the respective dimensions of sheet 60. This may be useful, forexample, for providing light directing properties to only a portion ofsheet 2. The free portion of sheet 60 may be used for purposed otherthan light redirection, e.g., for attaching sheet 2 to other structures.

According to one embodiment, sheet 60 may represent a planar glasswindow pane in a building façade and may be a part of opticallytransmissive glazing such as a wall window, a clerestory window, a doorwindow, a roof window, a skylight, and the like. In such a case, sheets4 and 40 may have identical dimensions with an area smaller than thearea of the glass pane (sheet 60) and thus cover only a certain portionof the pane. Sheets 4 may be first bonded to sheet 40 using opticallyclear adhesive layer 20 and the resulting sandwich of sheets 4 and 40may subsequently be laminated onto the surface of the window pane usingoptically clear adhesive 30. In an exemplary case of the material ofsheet 4 having a sufficiently high surface energy, surfaces 12 and 62may be attached to each other by means of intermolecular attraction(often referred to as “static cling” mechanism) and without the use ofadhesive layers.

Surface 12 may be specially configured to make sheet 4 attachable to asmooth glass surface by means of lamination. For this purpose, surface12 may be optionally calendered using is a series of hard pressurerollers to enhance its smoothness. In order to further enhance thelamination efficiency and/or adhesion to glass, surface 12 may bespecially treated for high surface energy or static cling properties,e.g., by using plasma, corona process or chemical treatment.

A predefined reference line 400 in FIG. 2 indicates the orientation ofchannels 6 in the finished sheet 2. Reference line 400 may have anysuitable orientation with respect to the edges of the sheet. It isgenerally preferred, however, that reference line 400 is parallel to oneof the edges of sheet 2.

In FIG. 3 illustrating an embodiment of rectangular sheet 2, referenceline 400 extends parallel to a shorted major dimension of sheet 2.According to an alternative embodiment, reference line 400 is parallelto a longer major dimension of the rectangular sheet 2.

The dimensions of light directing sheet 2 may vary in a broad range.Particularly, referring to FIG. 4, sheet 2 may be implemented in theform of a rectangular strip where the parallel channels 6 extendperpendicular to the longitudinal axis of the strip. In an alternativeconfiguration shown in FIG. 5, channels 6 extend parallel to thelongitudinal axis of the strip.

FIG. 6 illustrates the operation of sheet 2 in response to incidentlight, where a ray bundle 202 represents an off-normal parallel beam oflight entering surface 42 at an incidence angle 50 with respect to asurface normal 644. In the context of the present invention, the term“off-normal” is meant to characterize light rays having substantiallynon-zero incidence angles with respect to a surface normal, in contrastto “normal” rays having incidence angles equal to or substantially closeto zero with respect to the surface normal. It is noted that, in thecase of parallelism of all major surfaces of sheet 2, surface normal 644will also be a normal to the prevailing plane of the panel and to eachof its layers.

A portion of ray bundle 202 is intercepted by one of channels 6 andredirected by means of TIR from wall 7 of the channel. It willappreciated that, when walls 7 and 8 are properly separated from eachother by an air gap, the condition of TIR will generally be met for awide range of incidence angle 50, which can take values of up to 90°.Accordingly, such portion of ray bundle 202 may losslessly reflect fromthe respective wall 7 and exit from the opposing surface 64, asindicated by a ray bundle 204. It will be appreciated that, due to theparallelism of surfaces 42 and 64 and the perpendicularity of channel 6to such surfaces, ray bundle 204 will have an emergence angle (withrespect to normal 644) equal to the incidence angle 50 and will mirrorthe propagation path of ray bundle 202 in relation to the prevailingplane of sheet 2. Accordingly, the bend angle provided by sheet 2 issimply a function of the incidence angle 50. More particularly, the bendangle is generally twice the angle of incidence 50.

A ray bundle 206 represents a portion of ray bundle 202 that is notintercepted by the respective channel 6 and can thus be transmittedthrough sheet 2 without redirection, resulting in ray bundle 206maintaining the original propagation direction of ray bundle 202 uponthe exit from surface 64. Accordingly, the depicted configuration ofsheet 4 may be used to split an off-normal light beam into two beamspropagating away from each other at an angle equal to twice theincidence angle 50. It is noted that the relative distribution of energybetween redirected and transmitted light will mainly depend on thegeometry of channels 6 and the incidence angle 50. At a given incidenceangle, the proportions between the redirected and transmitted light willdepend on the ratio between the depth of channels 6 and their spacing.Accordingly, light redirecting properties of sheet 2 may be controlledby selecting the appropriate density at a given depth of channels 6 or,conversely, by selecting the appropriate depth of channels 6 at a givenspacing between individual channels.

A ray bundle 208 exemplifies light propagating along a normal directionwith respect to a surface of sheet 2. Since ray bundle 208 propagatesgenerally parallel to the plane of channels 6, each ray is transmittedby sheet 2 without any redirection. This illustrates the operation ofsheet 2 in which it provides for a generally unimpeded normal-incidencelight passage and can therefore have a substantially transparentappearance along the normal viewing direction. When a particularly goodview through sheet 2 is required, the width of each channel 6 may beadvantageously minimized to make such channels barely visible or eveninvisible by a naked eye. Obviously, minimizing the width of channels 6may also increase the useful light throughput of sheet 2 due tominimizing light interception by the edges of channels 6. Accordingly,it may be generally preferred that the average width of channels 6 isbelow 50 micrometers and may further be preferred that the channel widthis below 20 micrometers or even 10 micrometers.

Accordingly, sheet 2 represents an internally microstructured sheet-formstructure in which an array of deep and narrow channels 6 embedded intothe material of sheet 4 provides an angularly selective operation. Theangularly selective operation of sheet 2 in response to the incidence ofa light beam onto its major surface resulting in a portion of theincident light being either transmitted or redirected. The proportionsbetween the redirected and transmitted light is defined by the angle ofincidence and various parameters of channels 6.

FIG. 7 depicts an alternative configuration of sheet 2 in which surface64 used for light output is provided with surface microstructures 18configured for scattering light across a predefined angular range. Suchmicrostructures may be formed by a variety of suitable means andmethods, including but not limited to microreplication, embossing,molding or etching of surface 64. Alternatively, suitablemicrostructures 18 may be formed in an optically transmissive film whichcan be attached to otherwise smooth surface 64.

Microstructures 18 may be particularly configured to “soften”, diffuseor otherwise redistribute light redirected and transmitted by sheet 2.Alternatively, or in addition to this, microstructures 18 may beconfigured to blur the view for privacy and/or provide decorativefunctions. Various finishes and patterns commonly used for decorative orlight diffusing panels may be formed using microstructures 18, includingbut not limited to matte, microlens, prismatic, diamond, and “frostedglass”. Such microstructures may also be arranged in strips, blocks orvarious other geometrical or ornamental patterns.

Channels 6 may be formed in sheet 4 by any suitable technique that canproduce walls 7 and 8 with sufficiently smooth surface for TIRoperation. According to one embodiment, a preferred method of makingsheet 2 may include the steps of slitting one of the surfaces of sheet 4so that a plurality of parallel linear slits is formed that surface,stretching the sheet along a direction perpendicular to the linear slitsso that the opposing walls of each slit can be separated from eachother, and bonding such surface to a rigid sheet so that the opposingwalls separated apart in the previous steps can be permanently fixed inthat state and can form stable, yet narrow channels 6. Such method isillustrated in FIG. 8a -d.

Referring to FIG. 8a , a rotary blade 9 is used to slit surface 10 andform a plurality of parallel linear slits 14 that extend deep into thematerial of sheet 4.

Blade 9 penetrates relatively deep into the material of sheet 4 andmakes the cut by wedging the material out to the sides on its way. Theelasticity and easy deformability of the material is essential since itpermits for a relatively easy cut formation. The material deformselastically and relatively easily yields under the cutting pressure,leaving a clean cut without chipping, crazing or irregular tearing. Theelastic-type of the deformation on the cutting pressure of blade 9 alsoensures that the material returns to its original shape after slittingin the respective area and that channels 6 are formed with straight andparallel walls.

Accordingly, it is preferred that the material selected for sheet 6 hasa sufficiently high elastic range. The elastic range can be defined asthe maximum deformation (or strain) at which a material reaches itsyield strength (or the so-called proportional limit). In other words,the elastic range represents the maximum deformation (e.g., elongationalong a length direction) of the material at which the material is stillcapable to return to its approximate original dimensions using itselastic properties after the stress is removed.

The elastic range can be expressed in terms of a relative elongation ofthe material with respect to its original length. According to oneembodiment, the material of sheet 4 is configured to have an elasticrange of at least 10% of its original length, more preferably at least30%, even more preferably at least 50%, and even more preferably, atleast 100%.

On the other hand, it is preferred that the material of sheet 2 isrelatively soft to allow for deep blade penetration without breakage orpremature dulling. The hardness typical to most grades of TPU orplasticized PVC at room temperatures can be deemed appropriate for theformation of TIR-quality slits. More generally, the material of sheet 4should preferably have hardness that is below a durometer hardness valueof 95 Shore A (as measured in accordance with ASTM D2240 type A scale)at the time of slitting or at least does not significantly exceed suchvalue. If the plastic material is not sufficiently soft at roomtemperature, it should be heated and softened before the slittingprocess begins.

Referring further to FIG. 8a-d , the slitting process is repeated untilslits 14 cover all of the designated area of surface 10 (FIG. 8b ).Sheet 4 or its select areas may be pre-heated before slitting in orderto further soften the material of the sheet and enhance blade 9penetration into the material. In order to facilitate the slittingprocess, sheet 4 can also be stretched along a direction perpendicularto the slitting direction before or during the slitting process.

Blade 9 should be sufficiently sharp with a sub-micrometer curvatureradius of the tip, burr-free and made from a hard material. The surfaceof blade 9 at least near the cutting edge should be highly polished to avery low level of surface roughness. In one embodiment, the average RMSsurface roughness parameter of the surface of blade 9 near the cuttingedge should preferably be below 100 nanometers and, even morepreferably, below 50 nanometers. The average radius of curvature and thepeak to valley RMS surface roughness of the tip of the cutting edgeshould also be preferably less than 50 nanometers, more preferably, lessthan 20 nanometers, and even more preferably, less than 10 nanometers.

The penetration depth of blade 9 into sheet 4 is primarily defined bythe desired depth of the slits 6 to be formed in the sheet. According toone embodiment, the slitting depth should be greater than 25% of thethickness of the sheet material, and more preferably, greater than 50%.On the other hand, the slitting depth should not generally exceed 95% ofthe overall thickness of the material so that sheet 4 could retain itsstructural integrity.

Referring to FIG. 8c , sheet 4 is stretched along directions 582 and 584which are generally perpendicular to linear slits 14. A heat source 550may be used to soften the material of sheet 4 and facilitate itsstretching and reduce the load needed to obtain the required elongation.The elongation of sheet 4 in response to such stretching results in theseparation of walls 7 and 8 of each slit 14 thus forming narrow channels6. Such elongation may occur in an elastic deformation mode, a plasticdeformation mode, or a combination thereof.

It will be appreciated that, since the effective thickness of thematerial in the areas below each slit is considerably smaller than thetotal thickness of sheet 4, the elongation will generally be greater insuch areas compared to the adjacent “full thickness” areas. Accordingly,such disproportional elongation of sheet 4 along directions 582 and 584will favor forming channels 6 and will require applying considerablylower stress compared to the case of stretching sheet 4 when it isintact.

Referring to FIG. 8d , rigid sheet 40 is bonded to surface 10 of sheet 4using optical adhesive layer 20 while sheet 4 is in the elongated orstretched state. The stiffness of sheet 20 should be sufficient toprevent the relaxation of sheet 4 into its original length along thestretch direction. Accordingly, walls 7 and 8 of channels 6 can bepermanently separated from each other even if sheet 4 was stretched inan elastic deformation mode. This prevents closing the walls of eachchannel 6 upon each other and disrupting their TIR operation.

Referring to FIG. 8d , rigid sheet 60 is bonded to the opposing surface12 of sheet 4 using optical adhesive layer 30, thus completing theformation of sheet 2. There are a number of suitable techniques that canbe used for bonding rigid sheets 40 and 60 to the soft and flexibleinner sheet 4, which may include but are not limited to roll lamination,press lamination, vacuum press lamination, encapsulation and the like.The bonding process may also include curing the adhesive layers 20and/or 30 using heat, moisture, UV light or other techniques dependingon the type of adhesive used.

The outer layers 40 and 60 may also be bonded to the inner sheet 4 usinga suitable technique which does not involve any adhesives. Examples ofsuch bonding include but are not limited to heat welding, ultrasonicwelding, radio-frequency (RF) welding, solvent welding and the like.

It should be understood that the above-described sequence of steps in amethod of making panel 4 is not prescriptive and may be modified on caseby case basis. For example, in one embodiment, sheet 4 may be bonded orlaminated to sheet 30 before bonding to sheet 40. Alternatively, sheet 4may be encapsulated by a simultaneous bonding or lamination of layers 40and 60 to respective surfaces 10 and 12. In one embodiment, the step ofstretching sheet 4 along directions 582 and 584 (FIG. 8c ) may precedethe step of slitting surface 10 of such sheet (FIG. 8a ). In this case,slitting of surface 10 using blade 9 may immediately result in theproper separation of walls 7 and 8 and the formation of channels 6without the need of additional stretching of sheet 4.

In a further modification of the method of making sheet 2, heat source550 can be adjusted to deliver temperatures to sheet 4 that aresufficient for annealing its material and permanently fixing the widthof channels 6 that was formed during the material stretching. Sheet 4can be exposed to such elevated temperature for a period of timesufficient to convert of at least a portion of the elastic deformationinto the plastic one. Such annealing can be advantageous for removingthe residual stresses in the finally formed sheet 2 and preventing itswarping of the slippage of sheet 4 between sheets 40 and 60.

Referring back to FIG. 8a , if the material of sheet 4 has a glasstransition temperature T_(g), the working temperature for the slittingprocess should generally be considerably greater than T_(g). At leastsome optically clear plastic materials, such as TPU orhighly-plasticized PVC, often have T_(g) which is significantly lowerthan the room temperature and may allow for proper slitting of sheet 4without additional heating. However, even in this case, heating sheet 4to above the room temperature may still be useful, for instance, forminimizing the wear of blade 9, reducing its friction with the materialsbeing slit or for enhancing the quality of the slits. In a non-limitingexample, when sheet 4 is made from a material with T_(g) of around 5°C., the working temperature may be set to 30° C. or more.

It will be appreciated that, as the temperature gradually increases andreaches a certain temperature, at least some polymeric materials wouldlose their stiffness and becomes elastic like a rubber. Accordingly, themethod illustrated in FIG. 8a-d may be extended to include processing ofplastic materials that are rigid or semi-rigid at room temperature. Byheating such materials during the steps of slitting and/or elongation ofsheet 4 in the elastic or plastic-elastic mode, suitable arrays ofparallel channels 6 may be produced. Accordingly, the inner sheet 4including TIR reflectors may be formed from such rigid or semi-rigidmaterials without departing from the general scope of this invention.

The arrangement of parallel channels 6 in sheet 4 is not limited toforming an array of such channels extending parallel to a particularreference line. Sheet 4 may also include other arrays of channels 6crossed an angle to that array. Referring to FIG. 9, a first array ofchannels 6 extends parallel to reference line 400 and a second array ofchannels 6 extends parallel to a reference line 401, where referencelines 400 and 401 are perpendicular to each other. It will beappreciated that such configuration of sheet 4 with two perpendiculararrays of channels 6 may be used for redirecting light in two orthogonaldirections.

Such perpendicular arrays of channels 6 may be formed in the same layerof sheet 4, as illustrated in FIG. 10. Alternatively, sheet 4 may beformed by two or more layers superimposed on one another and therespective arrays of channels 6 may be formed in those different layers.For example, referring to FIG. 11, sheet 4 may include a layer 304 wherethe first array of parallel channels 6 is formed and a layer 306 wherethe second array of parallel channels 6 is formed.

It is noted that all of the layers of sheet 2 materials can be made ofoptically clear materials with smooth surfaces in which case sheet 2 canbe made substantially transparent at least along normal or near-normalviewing directions. Since the proportions between transmitted andredirected light can be precisely controlled by the structure of sheet 4(e.g., by varying the channel spacing at a constant channel width) sheet2 can be configured to maintain at least some transparency even atoff-normal viewing angles. This is illustrated in FIG. 12 which shown anobject 988 that can be viewable through the light-redirecting sheet 2.

It is further noted that the appearance of sheet 2 may also beconfigured in a number of ways. For instance, a pigment may be added toits materials thus altering its color or transparency. Particularly, theoptical clarity either sheet of sheet 2 may be purposefully reduced sothat objects behind the sheet can be masked and/or blurred. In oneembodiment, one or more layers of sheet 2 may be tinted or configuredfor suitable light filtering properties, such as blocking of theinfra-red or ultra-violet rays, etc. Also, any suitable image or patternmay be printed on either surface of sheet 2 for decorative purposes. Theprint may be opaque or transparent/semitransparent and suitable printingtechniques may include but are not limited to digital printing, screenprinting, stencil-printing, selective dyeing and painting.

FIG. 13 schematically illustrates sheet 2 incorporated into a windowfilm 90 attached to a surface 80 of a glass window pane 300. Window pane300 exemplifies a window of a building façade exposed to the directand/or diffuse daylight. Layer 4 of sheet 2 is sandwiched between toplayer 40 of a rigid material and the glass pane 300.

Window film 90 incorporating sheet 2 can be attached to surface 80 usinga removable or permanent adhesive or using the so-called static cling.Suitable techniques for attaching film 90 to surface 80 may include butare not limited to the dry or wet lamination often used for applyingconventional window film products. A preferred mode of operation of suchwindow film 90 can be intercepting at least a portion of daylightincident from off-normal and redirecting such daylight to the ceiling soas to provide improved natural illumination to the building interiorwhile reducing the intensity of the transmitted solar beam and theassociated effects that can be unpleasant to the building occupants(e.g., intense heat and glare).

Sheet 2 can be sized to cover a top portion of window pane 300 so thatthe bottom portion of the window can be used for an unimpeded view ofthe outside. In this case, sheet 2 may include a textured surface todiffuse the injected beam of sunlight and maximize the uniformity oflight distribution within the illuminated space. Alternatively, sheet 2may be sized to cover essentially the entire surface 80 of pane 300 inorder to maximize solar beam filtering and redirection to the ceiling.In this case, sheet 2 may be configured for a maximum transparency so asto preserve the view. The thickness of sheet 2 can be selected from auseful range of film- and thin-sheet-thicknesses that would providesufficient handling convenience of window film 90 and simplify itslamination onto surface 80. In one embodiment, the thickness of sheet 2should not exceed 2 millimeters and more preferably should be below onemillimeter. The edges of the laminated window film 90 may be optionallysealed to prevent its delamination from surface 80 or moisture ingressbetween the film and window pane 300.

FIG. 14 schematically illustrates an embodiment of the present inventionin which sheet 2 is incorporated into a hanging window covering 70 thatis configured to provide daylight control and improve natural lightingof the building interior similarly to case where sheet 2 is attached tothe window surface (as described in reference FIG. 13 above).

Referring to FIG. 14, window covering 70 includes a rectangular sheet 2,a bar 530, and a pair of brackets 74 with two cords 72. Sheet 2 can havethe basic structure as shown in FIG. 1 and FIG. 2. Bar 530 can be shapedin the form of a rail or a tube extending above the window pane 300parallel to the ground.

Sheet 2 can be conveniently attached to bar 530 using brackets 74 and apair of cords 72. Bar 530 can be attached to the wall surrounding thewindow pane 300 or directly to such window pane and can be provided withthe associated hardware.

In one embodiment, sheet 2 of FIG. 14 is provided with a sufficientstiffness to maintain its generally planar shape by appropriatelyconfiguring the rigid layers 40 and 60. In one embodiment, sheet 2 maybe configured to have substantial flexibility so that it could maintaina planar shape under its own weight when it is hanging. An optionalweight bar (not shown) can be provided at the bottom edge of sheet 2 tohelp straighten up the sheet.

It is noted that the illustrated method of hanging sheet 2 in a closeproximity of window pane 300 is not prescriptive and can be replacedwith any other suitable method known in the art. For example, windowcovering 70 can have a general design and structure of a track panel

By way of example and not limitation, sheet 2 can replace the woven-typefabric or cloth in stationary or sliding window panels. A representativeexample of sliding panel window coverings can be the Skyline™ FR GlidingWindow Panels commercially available from Hunter Douglas Corporation. Arepresentative example of stationary panel window coverings can be theFreeform Fixed Shade commercially available from MechoSystemsCorporation. Similarly to the shadecloth, sheet 2 can be configured as aloose, flexible sheet trimmed to the size and shape of the windowopening or glazing and attached to a mounting bar using velcro stripsalong the edges or using any other suitable means.

In some implementations, window covering 70 may be arranged in multiplebands that are considerably narrower than the respective window pane.Such multiple bands can be hung alongside each other so as to cover theentire window area. Such multiple bands can also be incorporated intostationary or sliding window shade structure that can be operatedmanually using a chain, cord or wand or automatically using a gear motorand electronic control system.

Window covering 70 may also include various additional functional ordecorative layers. Such layer can include but are not limited to lightcontrol films, shadecloth, mini- or micro-blinds, and the like. Suchlayers can be co-laminated together with sheet 2, attached to sheet 2 inmultiple locations, or simply hung parallel to sheet 2 with or withouttouching the sheet.

In one embodiment, window covering 70 can be positioned in a slopedorientation so as to make a prescribed angle with respect to a verticalaxis. The slope angle can be advantageously selected provide an improvedlight control operation, such as enhanced daylight harvesting or directbeam shading. In case of a sloped window, the slope angle of covering 70can approximate the slope of the window pane. In one embodiment, theslope angle of window covering 70 is made adjustable with manual orautomatic control.

FIG. 15 schematically illustrates the operation of window covering 70when it is used for projecting daylight deep into the building interiorand redistributing the injected daylight for improved indoor naturallighting while reducing glare caused by the direct solar beam. Thebuilding interior is exemplified by a room 366 having a rectangularconfiguration and a window opening 500 within an external wall 847.

The incident daylight is represented by a ray 272 passing through windowopening 500 into the room. Ray 272 may particularly exemplify the directsunlight or diffuse skylight which naturally propagates in a downwarddirection and therefore tends to directly illuminate only the floor areain a vicinity of the window or various objects nearby.

Window covering 70 incorporating a large-area sheet 2 is disposed in thepath of ray 272. Sheet 2 deflects ray 272 from its natural downwardpropagation direction and redirects it onto a ceiling 320 of room 366.

There are numerous ways of how sheet 2 may be positioned within or in aclose proximity to such opening 500. For instance, in addition to thearrangements discussed above in reference to FIG. 14, sheet 2 may befixed in a suspended position by attaching its top edge to wall 847above opening 500, laminated onto a window pane, stretched between twoopposing rollers or bars, etc.

The ceiling 320 further scatters and redistributes the redirected ray272 thus enhancing the illumination level and improving lightingdistribution within room 366. Redirecting daylight onto the ceiling hasa number of advantages. For instance, considering that the incidencedirection of daylight changes in a very broad angular during the daytimeand seasonally, the large area of the ceiling and its typically uniformlight scattering characteristics across the surface ensures that ray 272is intercepted and properly scattered. Furthermore, since the ceiling isoften painted white or in relatively light colors, it may generally havea higher albedo (reflection coefficient) than the floor or variousobjects in the room interior. As a result, the light energy of ray 272may be scattered by the ceiling with a relatively low loss compared toscattering from other surfaces in the room and thus ensure more completesunlight harvesting and utilization for daylighting purposes.

Additionally, it may be appreciated that the surface of a ceilingtypically has very good light diffusing properties. Therefore, thereflection of light rays from the ceiling will be primarily of a diffusetype which may result in a relatively homogeneous light distribution inthe room and in a reduced glare.

A yet further advantage of redirecting daylight to the ceiling or upperportions of the room interior is that such redirection effectivelycreates a diffuse source of daylight within the room well above the eyeheight rather than allowing the direct daylight to reflect or scatterfrom the lower surfaces and produce blinding glare. A yet furtheradvantage will be apparent when room 366 includes partitions or varioustall objects which may partially or totally obstruct natural daylightpenetration deep into the room interior. The elevated position of theceiling, well above the obstruction objects can thus ensure naturalillumination of the areas that are otherwise shaded and inadequatelyilluminated.

Accordingly, positioning sheet 2 in a close proximity or within opening500 may provide at least partial shading of the room interior and itsoccupants from the direct sunlight while using the ceiling to convert asubstantial portion of the direct beam into diffuse daylight emanatedfrom an overhead location and thus enhancing the overall daylightinglevel and improving light distribution in the room interior.

In one embodiment, window covering 70 may include one or more areas thatare free from channels 16 and are either opaque or configured to provideenhanced light filtering. For example, window covering 70 can bedimensioned to cover the entire window area with a top portion beingoptically transmissive and configured for light redirection to theceiling and a bottom portion being opaque and configured for shading thedirect solar beam and rejecting the associated excessive glare and/orheat.

In window covering 70, one or more sheets of different materials can beattached to one or more edges of sheet 2. Such additional sheets canserve different purposes. Referring to FIG. 16, a top sheet 690 isattached to a top edge of light directing sheet 2 and a sheet 692 isattached to a bottom edge of sheet 2. Sheet 692 is made from an opaqueor translucent material which is configured for blocking or otherwiserejecting at least a portion of sunlight impinging onto its surface soas to reduce sunlight penetration into the building interior. It canconventionally be made from a fabric material or cloth used for windowshades. Accordingly, the lower portion of window covering 70 can operateas a conventional window shade while an upper portion of the coveringcan be used for enhanced illumination by redirecting the daylight to theceiling.

The top sheet 690 can also be made from a suitable fabric material butit can also have functions other than shading. In one example, it canhave a decorative function or provide edge-strengthening hemming for thetop edge of sheet 2. In another example, sheet 690 can be utilized forattaching sheet 2 to a headrail or other structure used to hang windowcovering 70 in front of a window.

FIG. 17 shows an embodiment of window covering 70 in which lightdirecting sheet 2 is made sufficiently flexible so as to allow witswrapping around relatively small objects. In one embodiment, sheet 2 mayincorporate just one layer formed by light-redirecting sheet 4 havingchannels 6 embedded into its body.

Window covering 70 of FIG. 17 further includes a top bar 772 having aU-shaped profile and provided with an insert 776 and a similarly-shapedbottom bar 774 provides with an insert 778. Such bars 772 and 774 areused to hold the opposing ends of sheet 2 so as to form a free-hangingwindow shade panel.

Inserts 776 and 778 are used for wrapping the respective ends of sheet 2around them in order to prevent material slippage from bars 772 and 774.The bottom bar should preferably have sufficient weight to slightlytension sheet 2 using gravity and prevent its excessive warping orwrinkling.

FIG. 18 shows another example of using light directing sheet 2 forilluminating building interior with daylight. Referring to FIG. 18, acanopy awning 800 is externally attached to a building façade above awall window in a slanted orientation. Awning 800 includes lightdirecting sheet 2 which is stretched over a rectangular frame 811 toform a relatively stiff panel. The panel is attached to wall 847 of thebuilding just above window pane 300 using support members 837 andbrackets 835 and is positioned at an angle to the horizon and to wall847.

Sheet 2 is oriented in such a way in the awning panel that thelongitudinal axis of the parallel array of channels 6 extends parallelto a horizontal plane. Each channel 6 is also formed perpendicular ornearly perpendicular to the surface of sheet 2.

By way of example and not limitation, the angle that the awning panel ismaking with respect to wall 847 can be around 45° which will positionthe individual planes of channels 6 at a 45° angle with respect to thevertical direction. Accordingly, when direct sunlight illuminates thestretched sheet 3 directly from the above (e.g., when the sun is nearits zenith), awning 800 will bend such sunlight at a right angle anddirect it towards window 300. Thus, awning 800 may be used foreffectively collecting sunlight from high sun's elevations and directingit into the building interior.

Such operation is further illustrated in FIG. 19, in which awning 800attached to wall 847 redirects light into the building interior troughwindow opening 500. Daylight is illustrated coming from high elevationsin which case the vertical window opening 500 generally cannot interceptmost of it. Awning 800 intercepts such daylight and directs it deep intothe room where the injected daylight is further scattered by walls andceiling. Such configuration of awning 800 may be useful, for example, toimprove the daylighting levels inside rooms which are obstructed fromsunlight by the nearby structures, such as high-rise buildings, talltrees, etc.

According to some embodiments, light directing sheet 2 may beincorporated into a skylight in a roof or ceiling of a building. This isillustrated in reference to FIG. 20 in which a ray 280 represents a beamof direct sunlight passing through a horizontal opening 502 in theceiling of a room 368 at an angle above 0° and less than 90° withrespect to a vertical direction. Such opening 502 may represent the exitaperture of a skylight of a roof window configured to illuminate room368 with daylight. Sheet 2 may have the structure of the above-describedembodiments and can incorporate a single array of parallel channels 6(not shown) or two or more parallel channel arrays crossed at an anglewith respect to each other where each of the embedded channels 6 isconfigured to reflect light by means of TIR. In addition, sheet 2 mayalso have light diffusing texture on one of its surfaces to spread boththe transmitted and redirected light.

In operation, by transmitting a first portion of the incident light beamand by redirecting a second portion of the light beam towards a sharplydifferent direction, sheet 2 of FIG. 20 distributes the light energy ofray 280 over a broad angular range. Due to the added light diffusingfeatures, sheet 2 can be configured to illuminate room 368 with arelatively uniform diffuse beam. In one embodiment, sheet 2 may beconfigured to produce a generally symmetric beam with respect to anormal to its surface at least at some off-normal incidence angles. Inone embodiment, sheet 2 may also be configured so that the respectivetransmitted and redirected light portions will have the angular span ofmore than 90° for at least some solar elevation angles so that theopposing portions or corners of room 368 may be adequately illuminated.

FIG. 21 illustrates a yet further embodiment of the invention andanother example of using the light directing sheeting of this invention.Referring to FIG. 21, one or more sheets 2 are attached to alight-emitting opening of a tubular skylight 542 in a verticalorientation. Skylight 542 exemplifies a conventional dome-shapedskylight in a building 370 with a tubular light guide that delivers thedome-captured daylight to the building interior. Channels 6 (not shown)should preferably be oriented horizontally so that daylight harvested byskylight 542 and emitted into the space below is intercepted andredirected to the adjacent areas of the ceiling for an indirectillumination of the space interior. As further shown in FIG. 21, somerays, particularly those propagating along vertical directions, may beallowed to exit from the opening of skylight without redirection thusproviding direct illumination as well. Accordingly, FIG. 21 isillustrative of using sheets 2 to form direct/indirect lighting fixturesand luminaires for skylights and other types of downlights.

FIG. 22 shows an embodiment of a prismatic skylight 552 having sheet 2attached to a sloped face 554 of its prism-shaped dome. Sheet 2 ispreferably attached an inner surface of face 554 to protect it from theenvironment. Sheet 2 can be applied to such surface by means oflamination or using any other suitable method. Although a small air gapcan be provided between sheet 2 and face 554 in some cases, it may bepreferred for most cases that there is a close physical and opticalcontact between sheet 2 and face 554.

In operation, a ray 902 exemplifying low-angle sunlight impinges ontoface 554 and passes through sheet 2 while experiencing redirectiondownward by a relatively high bend angle due to the interaction with TIRchannels 6 (not shown). Such operation can be advantageous, for example,for enhanced harvesting of low-elevation sunlight, such as thatoccurring in early morning or evening hours or during winter in theNorthern hemisphere. By bending the light ray 902 from an obliquepropagation to a near vertical propagation direction, skylight 552 canensure that such ray will be more efficiently transmitted into theinterior of a room 372. The vertical or near-vertical propagation can beparticularly advantageous in the case when skylight 552 includes a wellor a shaft that can scatter or absorb some light at each reflection. Insuch a case, the vertical or near-vertical light propagation minimizesthe number of reflections and can thus minimize the transmission losses.

A light ray 904 exemplifying sunlight incident from intermediate solarelevations is partially transmitted and partially redirected by sheet 2into a downward direction, as illustrated by ray segments 906 and 908,respectively. Accordingly, in late-morning or afternoon hours or duringspring or fall seasons, skylight 552 could redistribute the harvesteddirect sunlight into a broad angular range while still providingrelatively high light transmittance.

A light ray 910 exemplifying a direct solar beam at around noon insummer time is deflected by sheet 2 by a relatively high angle and canthus be either scattered or even rejected. Accordingly, such operationcould be advantageous for sunny climates with hot summers where suchrejecting or filtering of the excess sunlight (and thus the associatedheat) at high solar elevations could improve the occupants' comfort andreduce the space cooling load.

It is generally preferred that the slope angle of face 554 with respectto a horizontal plane is between 10° and 50° and more preferably betweenabout 20° and 45°. According to one embodiment, the slope angle of face554 is approximately 45°. According to one embodiment, such slope angleis approximately 35° or at least in a 30°-40° angular range. Accordingto one embodiment, face 554 is approximately facing a south direction.According to one embodiment, face 554 is facing an east direction.According to one embodiment, face 554 is facing west direction.

FIG. 23 shows an embodiment of a greenhouse structure 374 that has agenerally transparent roof with a first sloped face 376 facing south anda second sloped face 378 facing north. Such greenhouse structureexemplifies a conventional greenhouse used in horticulture andparticularly exemplifies a gable roof greenhouse structure witheast-west orientation of its longitudinal axis.

Greenhouses are passive solar structures intended to trap heat from thesun while also admitting natural daylight to the crops usinglight-transmitting glazing. Many plants require significantly more lightfor efficient growth than it is normally available in existinggreenhouse structures and require supplemental lighting or enhanceddaylighting. On the other hand, in year-around greenhouses located inclimates with hot summers, a problem exists of reducing the excess lightand heat penetration into the greenhouses in summer time. Accordingly,capturing more sunlight with the existing greenhouse structures whensuch sunlight is scarce and/or rejecting the excess heat at other timescould have a direct positive effect on energy saving and crop yield. Byemploying the light redirecting structure of sheet 2, harvesting oflow-elevation sunlight and filtering of high-elevation sunlight can beaccomplished thorough a relatively simple retrofit in which sheet 2 isattached to a surface of the existing glazing or otherwise incorporatedinto such glazing.

Referring to FIG. 23, face 376 of the greenhouse glazing has lightdirecting sheet 2 attached to a portion of its inner surface. Similarlyto the prismatic-type skylight structure 552 of FIG. 22, the greenhousestructure 374 is configured to harvest low-elevation sunlight asillustrated by the paths of light rays 1902 and 1904 and reject orscatter high elevation sunlight as illustrated by a light ray 1910.

A light ray 1960 exemplifies low-elevation sunlight incident intogreenhouse 374 through side walls or a lower portion of face 376. Thestructure of sheet 2 should preferably be designed to result inredirecting the low-elevation sunlight towards a canopy line 1500 ofplants 1502 so that light rays that would otherwise miss the canopy line(e.g., rays 1902 and 1904) could be directed to plants 1502 and couldalso superimpose with other incident rays (e.g., ray 1960) thuseffectively increasing the amount of light available to the plants. Inaddition to this, the structure of sheet 2 can be designed to redirecthigh-elevation sunlight away from the canopy line 1500.

Sheet 2 can be positioned parallel or at an angle to face 376 by meansof hanging or stretching using suitable frame members (not shown)Alternatively, sheet 2 can be laminated onto the inside surface of face376. Sheet 2 may also be sized to cover only a top portion of face 376or the entire surface of face 376. According to one embodiment, sheet 2covers at least a third of the surface of face 376 and the coveredsurface includes at least a top portion of the surface of face 376.

In the illustrated east-west orientation of the longitudinal axis andrespectively north-south orientation of opposing faces 378 and 376 ofgreenhouse structure 374, such greenhouse can be configured to captureadditional sunlight for plants 1502 in winter time (when such sunlightis particularly at premium). It can be further configured to reduce heatintake in the summer by providing enhanced light filtering and a partialshade due to redirecting a portion of incident light away from plants1502 and out of the greenhouse structure. In an alternativeconfiguration, a northern portion of the greenhouse structure 374 may beprovided with a mirrored film to minimize light spillage at low solarelevations or capture additional direct sunlight in winter time. Forexample, a portion of face 378 can be covered such mirrored film.

In a north-south orientation, such greenhouse structure 374 can beconfigured to provide enhanced illumination of plants 1502 in earlymorning or late evening hours while rejecting or filtering the excesslight and heat around the noon time. This is illustrated in FIG. 24 inwhich a second sheet 2 is attached to an opposing face 378 of greenhousestructure 374. Face 378 is facing east and is configured to captureadditional daylight in morning hours while face 376 is facing west andis configured to capture additional daylight in evening hours.

It is noted that, although light directing sheet 2 may be conventionallyrectangular or square and may be made in forms of a large-format sheetor a roll, it may be cut to any size or shape using any suitable cuttingtechnique to fit a particular application. Sheet 2 may also be bent toany suitable shape or wrapped around an object or a volume. In at leastone embodiment, sheet 2 may be formed into a closed cylindrical,conical, or pyramidal shape. Alternatively, multiple sheets 2 may beconnected together to form such shapes.

FIG. 25 shows an embodiment of a lighting diffuser lens 750 which can beattached to a light-emitting opening of a skylight or an electricaldownlight and which can be used for direct/indirect lighting accordingto the principles illustrated in FIG. 21. Diffuser lens 750 includesfour rectangular light directing sheets 2 connected at their edges thatare perpendicular to the linear channels 6. The resulting structureforms a hollow cylindrical shape with a rectangular cross-section andtwo opposing openings. As illustrated by exemplary light rays 192 and194, light can be input into diffuser lens 750 through any of the twoopenings. In operation, upon the passage through the respective sheets2, rays 192 and 194 are intercepted by embedded channels 6 andredirected at a bend angle being twice the angle of incidence. It willbe appreciated that, when diffuser lens 750 is attached to a directionallight source, it can communicate a very broad angular distribution tothe emitted light, well beyond the angular range of the light source,which may be advantageously used for providing indirect illuminationusing such sources.

FIG. 26 shows diffuser lens 750 configured in the form of a truncatedpyramid. FIG. 27 and FIG. 28 show diffuser lens 750 configured in theforms of a cylinder and a truncated cone, respectively. One or moreportions of sheets 2 may be left free from channels 6 for decorative orvarious other functional purposes.

FIG. 29 shows an embodiment of a recessed downlight module 98 employingdiffuser lens 750 in either one of the configurations of FIG. 25 andFIG. 27. Such downlight module 98 includes a light source 97 which canbe one or more light emitting diodes (LED), compact fluorescent lamp orany other type of light source. Module 98 may further include acollimating or otherwise beam-shaping lens 99 configured to direct lightdownwards within a prescribed angular cone.

In operation, downlight module 98 emits a cone of light in a downwarddirection. At least a portion of such light is intercepted by one ormore sheets 2 of diffuser lens 750 using embedded TIR reflectors ofchannels 6 and is redirected to a ceiling 760. Ceiling 760 furtherscatters the redirected light into different downward directions. Sincediffuser lens 750 blocks at least a substantial part of light rays fromthe direct propagation from downlight module 98 while redirecting therespective rays to the ceiling for indirect illumination, the apparentbrightness of the source and the associated glare may be considerablyreduced without appreciable reduction of the overall light output. Whenthe reflectivity of ceiling 760 is not sufficient for high efficiencyreflection, the ceiling area surrounding downlight module 98 may becovered with a bright light diffusing material to reduce energy losses.In one embodiment, sheet 2 of diffuser lens 750 may be made from anoptically transparent material and provided with smooth outer surfaces.In one embodiment, such sheet 2 may be provided with light diffusingfeatures such as surface texture or a light diffusing material tofurther mask the light source or improve light distribution pattern.

FIG. 30 depicts an embodiment of the light directing sheeting of thepresent invention which is exemplified by a slat 600 of vertical blindsor curtain. Slat 600 is formed by a strip of a flexible, optically clearmaterial which preferably has a thickness of less than 3 mm. In oneembodiment, slat 600 has the layered structure of sheet 2 shown in FIG.1.

Slat 600 is defined by opposing broad area surfaces 42 and 64, opposingterminal edges 611 and 613, and opposing side edges 615 and 617. Slat600 has a plurality of embedded TIR reflectors formed by a parallelarray of channels 6. In an exemplary non-limiting case, the TIRreflectors are formed in a strip of 0.08 inch (around 2 mm) opticallyclear plasticized PVC sheet material which is sandwiched between twoother identically shaped strips of optically clear, rigid plasticmaterial. Clear plasticized PVC strips are commercially available, forexample, from Tap Plastics in the form of clear vinyl strips having awidth of 8 inch and sold by the foot. Similarly to conventional verticalblind slats, slat 600 may have a through notch 609 which can be used forattaching the slat to a headrail or other-type horizontal structures.

Referring further to FIG. 30, channels 6 are formed in one of thesurfaces of the PVC-P core strip while the other surface of the stripmay be made generally uninterrupted and smooth. Channels 6 are formedperpendicularly to the longitudinal axis of the strip andperpendicularly to the strip surface so that wall 7 of each slit isfacing up and the respective opposing wall 8 is facing down. Channels 6may extend all the way across slat 600 from its side edge 615 to theopposing side edge 617. Each of the walls 7 and 8 may be configured forspecular TIR functionality. The surfaces of the slits can be made eitheroptically smooth or may have a relatively low roughness so that they canreflect light by means of TIR primarily in the specular regime. If thesurface of walls 7 and 8 has some residual roughness and at least somelight is reflected in a diffuse regime, it is preferred that such lightis reflected within a narrow angular range from the specularly reflectedbeam.

One of the broad-area surfaces 40 and 64 may be configured for lightinput and the one can be configured for light output, respectively. InFIG. 30, the operation of slat 600 is illustrated where surface 42 isoperating in a light input mode and surface 64 is operating in a lightoutput mode. At least some light rays entering into slat 600 fromnon-zero sun elevations are intercepted by the TIR surfaces of walls 7and redirected into the building interior by reflecting primarily in aspecular regime. Accordingly, the daylight is injected into the buildinginterior at an angle which favors illumination of the upper portions ofthe room, such as ceiling and tops of the walls. In turn, the diffusereflections from the ceiling and the walls may further redistribute thedaylight through the interior thus resulting in improved lightinguniformity.

FIG. 31 shows an exemplary arrangement of an array of slats 600 in avertical blinds structure 700. Each slat 600 is attached to a headbox711 in a suspended position. Headbox 711 may be conventionally fixedatop of a window frame or a door frame in a daylit building facade andmay include a sliding headrail for deploying and retracting the blinds.Headbox 711 may further include a rotating drum by means of which slats600 may be opened and closed. A wand 713 may be provided to effectuatethe manual control of the blinds. Alternatively, a pull cord or anyother means for manual or electrical control of the blinds may be used.

It will be appreciated that, when slats 600 are in a suspended position,each internal TIR surface formed by channels 6 in such slats will begenerally parallel to the horizontal plane in any allowed slatorientation. Thus, in operation, when the blinds structure 700 is fullydeployed and slats 600 are closed, daylight can enter into the roomwhile being advantageously redirected by horizontal channels 6 towardsthe ceiling and can thus be redistributed through the interior moreefficiently. When slats 600 are fully retracted or open, little or nodirect sunlight will be intercepted and redirected by the slats.Accordingly, the daylighting operation of the vertical blinds structure700 and the distribution of daylight in the building interior may becontrolled by simple operations such as deploying, retracting, openingor closing of the blinds.

According to one embodiment, a strip of light directing material havingthe structure of sheet 2 may be incorporated into horizontal venetianblinds structure. In this case, one or more slats of the horizontalblinds may be formed by a strip-shaped sheet 2 where, unlike thevertical blinds slat of FIG. 30, each channel 6 can extend parallel tothe longitudinal dimension of the strip so that the configuration of theslat will be similar to that of FIG. 5. Such horizontal slat may havenotches formed at least the ends of the respective strip for passing asupport cord through them.

An embodiment of a horizontal window blinds structure 900 is illustratedin FIG. 32 showing a partial view of four slats 920 adjustably operableby cords 912 and 914. Each of the slats 920 has a slightly curved shapefor structural rigidity and incorporates a light redirecting structureof sheet 2. Depending on the orientation of slats 920, blinds structure900 may be configured to either reject the direct sunlight or redirectit into the building interior at a prescribed angle.

As illustrated in FIG. 33, when slats 920 are in a fully open position,a light ray 922 exemplifying a beam of direct sunlight strikes one ofthe slats 920 and is redirected back towards the exterior of a buildingusing channels 6 embedded into sheet 2. Accordingly, such operation ofblinds structure 900 may be useful for rejecting at least a portion ofthe solar beam from entering the building interior and thus reducing theheat gain and glare associated with direct sunlight. It is noted that,unlike conventional window blinds which require to be closed for blockthe sunlight penetration (thus also blocking the view), blinds structure900 may achieve similar sunlight rejection results while essentiallypreserving the view. The view preservation is illustrated by theunimpeded path of a ray 924 exemplifying light incident into thebuilding interior from various outdoor objects.

When slats 920 are in a fully closed position (FIG. 34), the directsunlight is redirected to the ceiling (as shown by the path of ray 922)while the view may still be at least partially preserved (ray 924),depending on the transparency of the material of slats 920. In oneembodiment, various light diffusing features, such as surface texturingor the like, may be purposefully employed in slats 920 to increase theangular spread of the admitted light at the expense of the slattransparency.

Slats 920 may be adjusted to any intermediate angular orientationbetween the fully open and fully closed position in which case theamount of rejected and/or admitted light can be controlled for almostany solar elevation. It is noted that, similarly to the conventionalvenetian blinds, blinds structure 900 may be configured so that slats920 can be rotated almost 360 angular degrees and either concave orconvex surfaces of the slats may be exposed to the incident sunlight. Itis further noted that, by adjusting the angular position of slats 920,the angular direction of the admitted daylight with respect to ahorizontal plane may be varied in a broad range. Such operation isillustrated in FIG. 35 in which ray 922 is redirected at a considerablyshallower angle with respect to a horizontal plane compared to theincident direction. This can be useful, for example, for illuminatingdeep portions of the building interior by steering such redirected lightfarther away from the window.

FIG. 36 shows an embodiment of a skylight 544 having a top portioncovered with a clear dome and having sheet 2 positioned within suchdome. Light directing sheet 2 forms a light redirecting insert that canbe configured to enhance light harvesting and light delivery efficiencyof the skylight. Skylight 544 may exemplify a tubular skylight, althoughthe same operation of sheet 2 in FIG. 37 may be applied withoutlimitations to other types of skylights.

Light directing sheet 2 of skylight 544 may have a rectangularconfiguration which can be planar or bent to a slightly curved shape.Sheet 2 is positioned at an angle with respect to a horizontal planewhich is preferably below 45°, and more preferably is within a 5°-35°angular range. Such sheet 2 may be mounted in a fixed position at apreselected slope angle which is optimized for specific geographicallatitude and oriented with its light-receiving surface 42 facing south.It may also be rotatably mounted to provide with single- or dual-axissolar tracking. In one embodiment, light directing sheet 2 can berotated around a horizontal axis. Alternatively, or in addition to that,sheet 2 can be rotated around a vertical axis.

In operation, a low-elevation light ray 472 striking sheet 2 isredirected downwards along a vertical direction. A high-elevation ray474 passes through sheet 2 without being redirected. An oppositelow-elevation ray 476 enters skylight 544 with its light path unimpededby sheet 2. Accordingly, the light redirecting insert formed by sheet 2intercepts and redirects at least a portion of sunlight that is incidentonto the light receiving aperture of skylight 544 from low-elevationangles. It will be appreciated that, for a tubular skylight, redirectinglow-angle light towards the vertical will typically increase the lightoutput on the exit side due to fewer reflections from the mirrored wallsof the skylight's light-guiding tube.

Strips of light redirecting sheet 2 may be used to form differentconfigurations of slats, louvers or vanes which can be incorporated intoa broad variety of daylighting systems and configured to improvesunlight harvesting efficiency. FIG. 37 shows one embodiment of skylight544 in which vanes 560 are positioned within the skylight dome in asloped orientation with respect to a light receiving aperture of theskylight. Each vane 560 is formed by a strip of light redirecting sheet2 or incorporates such sheet as one of its layers.

Each of the vanes 560 is positioned at a predefined angle (slope angle)with respect to a horizontal plane. Such slope angle may be the same foreach vane 560 or it may be different for each vane. According to oneembodiment, the slope angle should preferably be between 0° and 45°, andmore preferably between 5° and 30°.

In one embodiment, vanes 560 may be oriented horizontally and faced thesouth in northern hemisphere or the north in the southern hemisphere tomaximize daylight capture in winter or in summer, respectively.Alternatively, vanes 560 may be faced towards the east or west tomaximize daylight harvesting in the morning or evening hours,respectively.

Referring to FIG. 37, a light ray 572 exemplifying direct sunlightincident onto the light receiving aperture of skylight 544 from lowsolar elevations strikes one of the vanes 560 and is redirecteddownwards. It will be appreciated that such operation will particularlybe advantageous for tubular skylights or skylights having a relativelydeep light-channeling tube, shaft or well which rely upon multiplereflections from their walls. Since the redirected ray 572 makes muchlower angle with respect to a vertical axis compared to the initialpropagation direction, it will undergo fewer reflections from such wallsand therefore can be delivered to the building interior with fewerlosses, thus improving the overall light output from the skylight.Considering that the number of reflections for low-elevation rays in atubular skylight can be substantial and that 5% to 25% of light energymay be lost at each reflection, redirecting such rays toward a verticaldirection may improve the skylight performance rather dramatically.

It is noted that, unlike specularly reflective vanes sometimes utilizedin skylights, vanes 560 can be made substantially transmissive for thenormal incidence rays (see. e.g., the path of a ray 574 in FIG. 37).Accordingly, such light redirecting component of a skylight will notblock light as the sun moves across the sky and the incidence anglechanges. At the same time, as illustrated by a ray 576, a low-elevationsolar beam incident from the opposing direction may freely pass throughthe spaces between vanes 560. A sufficient width S of each space betweenvanes 560 may be provided to minimize the interception of light by vanes560 when the incidence angle is not optimal. On the other hand, spacingS may be kept below a certain value to maximize the interception andredirection of light coming from low elevation angles.

Vanes 560 may be made stationary and permanently oriented towards apredetermined direction. Alternatively, vanes 560 can be made rotatablymovable around one or more axes. In one embodiment, each vane 560 ismade rotatable around a horizontal axis. In one embodiment, a group ofvanes 560 can be rotated around a vertical axis configuration. In suchconfiguration, the entire light-redirecting insert can be mounted on avertical shaft or placed on a turntable-type structure. Accordingly,vanes 560 may be configured for one- or two-axis solar tracking tomaximize sunlight capture daily and/or seasonally.

Vanes 560 may be arranged into two symmetrically disposed arrays, forexample, as shown in FIG. 38. Such configuration may be adapted for aneast-west orientation. In this case, each of the arrays may beconfigured to maximize the interception of low-elevation sunlight in themorning and evening hours, respectively.

The spacing areas between vanes 560 and the dimensions and parameters ofthe vanes may be designed so that that the skylight could provide anearly constant light output during the day. This can be achieved, forexample, by capturing more sunlight in early morning and late eveninghours and by rejecting a portion of sunlight when the sun is near itszenith, according to the principles similar to those discussed inreference to FIG. 22 and FIG. 23.

When the ability of a skylight to intercept low-angle light rays fromall-directions is desired, light directing sheet 2 or multiple pieces ofsuch sheet may be formed into a three-dimensional shape providing amulti-directional or omni-directional operation.

A multi-directional structure employing light-directing sheeting of thepresent invention is illustrated in FIG. 39 which shows an embodiment ofa light redirecting skylight insert 1100 which is designed to bepositioned within a skylight dome for capturing low-angle sunlight anddirecting it downwards. Skylight insert 1100 comprises light directingsheet 2 formed into a truncated pyramid with a square or rectangularbase. The dihedral angles of each face of such pyramid with respect tothe pyramid base should preferably be less than 45° and, morepreferably, between 20° and 35°. Such insert may be positioned within alight receiving aperture of a skylight and configured to improve lightharvesting for at least the low-elevation solar rays. The dihedralangles of the pyramid faces, the dimensions of the central opening andthe height of the truncated pyramid may be varied depending on theintended geographical location of the skylight and/or specificpreferences as to the light redirecting operation of insert 1100.

The pyramidal shape of skylight insert 1100 may be formed directly froma single sheet 2 pre-cut into an appropriate two-dimensional template.Alternatively, such structure may be formed from an opticallytransmissive sheet or rigid film material in which case individualsheets 2 may be laminated onto the respective faces of the structure.Furthermore, an appropriate skylight dome may be formed into suchpyramidal shape and such sheets 2 may be laminated directly onto theinside surfaces of the shape.

FIG. 40 shows an alternative configuration of insert 1100 which isformed into a truncated conical shape with a round base. In thisconfiguration, insert 110 can be configured to provide omni-directionaloperation. In further alternatives, insert 1100 may be formed into othershapes such as, for example, pentagonal, hexagonal or octagonaltruncated pyramids.

Such inserts 1100 may also be made in different sizes and arranged in anested configuration. FIG. 41 shows an array of three nested pyramidalinserts 1100. FIG. 42 shows an array of three nested conical inserts1100. It may be appreciated that each of such nested light redirectinginserts 1100 may have a cross sections similar to those of FIG. 39 orFIG. 40 and can provide multi-directional or omni-directional operationwith a relatively high coverage of the entrance aperture of therespective skylight.

It is noted that sheet 2 may be formed in any other suitablethree-dimensional shapes which are not limited to basic geometricalshapes. For this purpose, sheet 2 can be cut into appropriatetwo-dimensional templates that can be bent or otherwise formed intoself-supporting 3D structures.

FIG. 43 shows a two-dimensional template cut from sheet 2 in which oneedge 1092 is substantially straight and another edge 1094 is curvedcreating two intersection points on the template. Channels 6 are shownextending generally parallel to edge 1092.

FIG. 44 shows two symmetrically disposed inserts 1100 each formed from atemplate of FIG. 43 by bending such template along lines indicated inFIG. 43. Such inserts may accordingly be positioned within a lightreceiving aperture of a skylight in a symmetrical arrangement and may beoriented such that one inserts faces east and the other insert faceswest. A space may be provided between such inserts 1100. Such spacingcan be utilized, for example, to admit a portion of the incidentsunlight without intercepting and redirecting.

FIG. 45 shows a further variation of inserts 1100 which may be formedfrom a template in which edges 1092 and 1094 are both curved and havedifferent prevailing radii of curvature.

Further details of the structure and operation of light directingsheeting of the invention and the method for making the same, as shownin the drawing figures, as well as their possible variations will beapparent from the foregoing description of preferred embodiments.Although the description above contains many details, these should notbe construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. Therefore, it will be appreciated that the scope ofthe present invention fully encompasses other embodiments which maybecome obvious to those skilled in the art, and that the scope of thepresent invention is accordingly to be limited by nothing other than theappended claims, in which reference to an element in the singular is notintended to mean “one and only one” unless explicitly so stated, butrather “one or more.” All structural, chemical, and functionalequivalents to the elements of the above-described preferred embodimentthat are known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe present claims. Moreover, it is not necessary for a device or methodto address each and every problem sought to be solved by the presentinvention, for it to be encompassed by the present claims. Furthermore,no element, component, or method step in the present disclosure isintended to be dedicated to the public regardless of whether theelement, component, or method step is explicitly recited in the claims.No claim element herein is to be construed under the provisions of 35U.S.C. 112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for.”

What is claimed is:
 1. A daylight redirecting window covering,comprising: A thin and flexible optical sheet having a first broad-areasurface configured for light input, a second broad-area surfaceconfigured for light output, and a layered structure comprising a firstsheet of a rigid optically transmissive material, a second sheet of arigid optically transmissive material, and an intermediate layer of arelatively soft optically transmissive material bonded to the first andsecond sheets; a plurality of elongated TIR surfaces formed within thelayered structure, the TIR surfaces longitudinally extending parallel toan edge of the optical sheet and transversely extending between thefirst and second broad-area surfaces; a plurality of light scatteringsurface microstructures formed in the second broad-area surface andconfigured to spread light at least in a plane that is perpendicular toa common longitudinal axis of the plurality of elongated TIR surfaces;wherein the optical sheet is configured to partially transmit andpartially redirect a parallel beam of light toward a range of divergentdirections, wherein an angle between a propagation direction of at leastone transmitted light ray and a propagation direction of at least oneredirected light ray is greater than 90°.
 2. The daylight redirectingwindow covering of claim 1, wherein a durometer hardness of the materialof said layer is less than 95 Shore A.
 3. The daylight redirectingwindow covering of claim 1, wherein the material of said layer has anelastic range of at least 10%.
 4. The daylight redirecting windowcovering of claim 1, comprising a plurality of channels formed in thelayer of a relatively soft optically transmissive material, wherein eachof the plurality of channels has at least one surface extendingtransversely with respect to the first broad-area surface.
 5. Thedaylight redirecting window covering of claim 1, wherein the opticalsheet is attached to a surface of a window of a building façade.
 6. Thedaylight redirecting window covering of claim 1, wherein the opticalsheet is attached to a light transmitting surface of a skylightstructure.
 7. The daylight redirecting window covering of claim 1,wherein the optical sheet is configured to be hung or suspended withinor near an opening of a building facade.
 8. The daylight redirectingwindow covering of claim 1, wherein the optical sheet is adapted to beoperably retained in a bent or rolled configuration.
 9. The daylightredirecting window covering of claim 1, wherein the optical sheet isadapted to be operably retained in a horizontal orientation.
 10. Avenetian window blind structure, comprising: a plurality of slat memberslongitudinally extending parallel to each other and being rotatablymovable about one or more axes, each of the plurality of slat memberscomprising a sheet of an optically transmissive material, wherein saidsheet comprises a plurality of parallel TIR surfaces formed in theoptically transmissive material and configured to redirect at least aportion of sunlight incident onto said sheet toward a direction that isnot coincident with the original propagation direction.
 11. The venetianwindow blind structure of claim 10, wherein said sheet is configured topartially transmit and partially redirect a parallel beam of sunlighttoward a range of divergent directions, wherein an angle between apropagation direction of at least one transmitted light ray and apropagation direction of at least one redirected light ray is greaterthan 90°.
 12. The venetian window blind structure of claim 10,comprising a plurality of light scattering surface microstructuresformed a surface of the sheet and configured to increase the divergenceof the redirected sunlight.
 13. The venetian window blind structure ofclaim 10, wherein the optically transmissive material comprisesplasticized polyvinyl chloride.
 14. The venetian window blind structureof claim 10, wherein the optically transmissive material comprises alayer of a relatively soft and elastic material.
 15. The venetian windowblind structure of claim 10, wherein the optically transmissive materialcomprises a layer of a relatively soft and elastic material and at leastone of the TIR surfaces is formed in said layer.
 16. The venetian windowblind structure of claim 10, wherein said sheet comprises a layer of arelatively soft and elastic material that is sandwiched between a firstsheet of a rigid material and a second sheet of a rigid material. 17.The venetian window blind structure of claim 10, wherein a durometerhardness of at least one layer of the optically transmissive material isless than 95 Shore A.
 18. The venetian window blind structure of claim10, wherein at least one layer of the optically transmissive materialhas an elastic range of at least 10%.
 19. The venetian window blindstructure of claim 10, wherein at least one of said one or more axes ishorizontal.
 20. The venetian window blind structure of claim 10, whereinat least one of said one or more axes is vertical.